Light controlling sheet and surface light source device

Abstract

A light controlling sheet is provided in a surface light source device including a light source portion. The light controlling sheet includes an outgoing light side lens portion having multiple unit lenses arranged to project toward the outgoing light side, and transparent portions and reflecting portions provided on the incident light side. The transparent portions and the reflecting portions are arranged alternately, and the transparent portions comprise 40% to 60% of the total area of the light controlling sheet when viewed form a direction orthogonal to the sheet surface on the incident light side.

1. A light controlling sheet having a sheet surface provided in a straight-down type surface light source device including a light source portion, the light controlling sheet comprising:
 an outgoing light side lens portion having multiple unit lenses arranged to project toward an outgoing light side; 
 transparent portions provided on an incident light side; 
 an incident light side lens portion having a lens shape which projects toward the incident light side formed in each transparent portion; and 
 reflecting portions comprising areas other than the transparent portions on the incident light side; 
 wherein the transparent portions transmit light coming from the light source portion, the reflecting portions reflect light coming from the light source portion, the transparent portions and the reflecting portions are arranged alternately, and the transparent portions comprise 40% to 60% of a total area of the light controlling sheet when viewed from a direction orthogonal to the sheet surface on the incident light side so that the light controlling sheet uniformalizes and/or condenses light coming from the light source portion. 
 
   
   
     2. The light controlling sheet according to  claim 1 , wherein
 when assuming that a pitch of the arrangement of the unit lenses of the outgoing light side lens portion is P, a thickness from the surface of the transparent portions to the apex of the unit lenses of the outgoing light side lens portion is t, and an average refractive index of a material forming the light controlling sheet is n, the following relationship can be satisfied:
   sin −1 (1/ n )≦tan −1 ( P/t ). 
 
 
   
   
     3. The light controlling sheet according to  claim 1 , wherein
 each unit lens of the outgoing side lens portion is formed such that the unit lens is a part of an elliptical cylinder whose major axis is orthogonal to the sheet surface, or a part of a spheroid whose major axis is orthogonal to the sheet surface. 
 
   
   
     4. The light controlling sheet according to  claim 3 , wherein
 a semi-major axis of each unit lens of the outgoing side lens portion is in a range of 1.5 times to 3.0 times its semi-minor axis. 
 
   
   
     5. The light controlling sheet according to  claim 1 , wherein when assuming that the pitch of the arrangement of the unit lenses of the outgoing light side lens portion is P, the thickness from the surface of the transparent portions to the apex of the unit lenses of the outgoing light side lens portion is t, the average refractive index of the material forming the light controlling sheet is n, an angle defined between a tangent obtained at the lens surface of the incident light side lens portion at one end of each transparent portion and the sheet surface is θ, and an opening ratio which is an area ratio of the transparent portion is R, the following relationship can be satisfied:
   sin −1 (1/ n )−θ≦tan −1 {(2 −R )×0.5× P /( t−h )}. 
 
   
   
     6. The light controlling sheet according to  claim 1 , wherein when assuming that the pitch of the arrangement of the unit lenses of the outgoing light side lens portion is P, the thickness from the surface of the transparent portions to the apex of the unit lenses of the outgoing light side lens portion is t, the average refractive index of the material forming the light controlling sheet is n, and the opening ratio which is an area ratio of the transparent portion is R, the following relationship can be satisfied:
   sin −1 (1/ n )≦tan −1 {(2− R )×0.5× P/t}.   
 
   
   
     7. The light controlling sheet according to  claim 1 , wherein
 the reflecting portions project toward the incident light side as compared with the transparent portions. 
 
   
   
     8. The light controlling sheet according to  claim 1 , wherein
 the reflection portions are formed by printing or transferring. 
 
   
   
     9. The light controlling sheet according to  claim 1 , wherein the reflecting portions provide diffusion reflection of light. 
   
   
     10. The light controlling sheet according to  claim 1 , wherein when assuming that the surface area of the incident light side is Si, and the surface area of the outgoing light side is So, the following relationship can be satisfied:
   0.8 <Si/So< 1.2. 
 
   
   
     11. A light controlling sheet having a sheet surface provided in a straight-down type surface light source device including a light source portion, the light controlling sheet comprising:
 an outgoing light side lens portion having multiple unit lenses arranged to project toward an outgoing light side; 
 transparent portions provided on an incident light side; 
 a concave-convex shape comprising multiple convex portions and multiple concave portions each being interposed between each adjacent pair of the convex portions provided on the incident light side, so that an apex of each unit lens and a central portion of each corresponding concave portion are located at positions so that they are aligned with each other when viewed from a direction orthogonal to the sheet surface; and 
 reflecting portions comprising areas other than the transparent portions on the incident light side, formed on each convex portion; 
 wherein the transparent portions transmit light coming from the light source portion, the reflecting portions reflect light coming from the light source portion, the transparent portions and the reflecting portions are arranged alternately, and the transparent portions comprise 40% to 60% of a total area of the light controlling sheet when viewed from a direction orthogonal to the sheet surface on the incident light side so that the light controlling sheet uniformalizes and/or condenses light coming from the light source portion. 
 
   
   
     12. The light controlling sheet according to  claim 11 , wherein a projecting amount of the convex portions from the concave portions is within a range of 5 μm to 60 μm. 
   
   
     13. The light controlling sheet according to  claim 11 , wherein the unit lenses, the convex portions and the concave portions are integrally formed. 
   
   
     14. The light controlling sheet according to  claim 11 , wherein
 a ridgeline around the boundary between each convex portion and the adjacent concave portion is a gently curved face, and 
 wherein the reflecting portion is also formed on each curved face at the ridgeline. 
 
   
   
     15. The light controlling sheet according to  claim 11 , wherein a shape of each concave portion includes a curved face projecting toward the incident light side. 
   
   
     16. The light controlling sheet according to  claim 15 , wherein the curved face of each concave portion is formed such that an angle defined between a tangent obtained around its central portion and the sheet surface is a relatively small angle, while an angle defined between a tangent obtained at a position closer to each adjacent convex portion and the sheet surface is a relatively large angle. 
   
   
     17. The light controlling sheet according to  claim 15 , wherein the curved face of each concave portion is a shape of a part of an elliptical cylinder. 
   
   
     18. The light controlling sheet according to  claim 11 , wherein an apex of each unit lens and a central portion of each corresponding convex portion are located at positions such that they are aligned with each other when viewed from a direction orthogonal to the sheet surface, and
 wherein the reflecting portion is formed on each concave portion. 
 
   
   
     19. The light controlling sheet according to  claim 18 , wherein a depth of the concave portions from the convex portions is within a range of 5 μm to 60 μm. 
   
   
     20. The light controlling sheet according to  claim 18 , wherein a width on the outgoing light side of each concave portion is narrower than a width on the incident light side thereof. 
   
   
     21. The light controlling sheet according to  claim 18 , wherein
 a water-repellent layer is formed on each convex portion. 
 
   
   
     22. The light controlling sheet according to  claim 18 , wherein a shape of each convex portion includes a curved face projecting toward the incident light side. 
   
   
     23. The light controlling sheet according to  claim 22 , wherein the curved face of each convex portion is formed such that an angle defined between a tangent obtained around its central portion and the sheet surface is a relatively small angle, while an angle defined between a tangent obtained at a position closer to the adjacent convex portion and the sheet surface is a relatively large angle. 
   
   
     24. The light controlling sheet according to  claim 22 , wherein the curved face of each concave portion is a shape of a part of an elliptical cylinder. 
   
   
     25. A surface light source device for illuminating a transmission-type display portion from the back side, the surface light source device comprising:
 a light source portion including a plurality of light sources; and 
 a light controlling sheet comprising
 an outgoing light side lens portion having multiple unit lenses arranged to project toward an outgoing light side, 
 transparent portions provided on an incident light side, 
 an incident light side lens portion having a lens shape which projects toward the incident light side formed in each transparent portion, and 
 reflecting portions comprising areas other than the transparent portions on the incident light side; 
 
 wherein the transparent portions transmit light coming from the light source portion, the reflecting portions reflect light coming from the light source portion, the transparent portions and the reflecting portions are arranged alternately, and the transparent portions comprise 40% to 60% of a total area of the light controlling sheet when viewed from a direction orthogonal to the sheet surface on the incident light side so that the light controlling sheet uniformalizes and/or condenses light coming from the light source portion. 
 
   
   
     26. The surface light source device according to  claim 25 , wherein
 the light controlling sheet mainly controls light traveling along the vertical direction on a screen of a transmission-type display portion in use. 
 
   
   
     27. The surface light source device according to  claim 25 , further comprising:
 a diffusion sheet having a light diffusing property. 
 
   
   
     28. The surface light source device according to  claim 27 , further comprising:
 a second light controlling sheet adapted to mainly control light traveling along a direction orthogonal to the direction along which the light controlling sheet controls light mainly. 
 
   
   
     29. The surface light source device according to  claim 28 , wherein
 particles having a light diffusing property are added to at least one of the sheets contained in the surface light source device. 
 
   
   
     30. The surface light source device according to  claim 25 , wherein
 a highly rigid sheet having a rigidity higher than that of the light controlling sheet is provided on the light source side of the light controlling sheet. 
 
   
   
     31. The surface light source device according to  claim 30 , wherein
 the light controlling sheet is joined at its reflecting portions to the highly rigid sheet.